The invention relates to a method of continuously winding a saddle-shaped deflection coil flaring out from a rear end towards a front end, of the type whose front end has a flange-shaped connection portion extending transversely to the longitudinal axis, for use in picture display tubes, the longitudinal turns of the coil being distributed over a number of sections and each turn of a section surrounding the turns of the previous sections and each pair of adjoining sections being separated over a part of its length by at least one aperture which is formed in that a pin is introduced at the front end into the winding space in at least two positions which are symmetrical relative to the longitudinal axis along the boundary between the two sections and after providing the number of turns desired for the first of these two sections, whereafter the second section is wound around said pins. The invention also relates to a deflection system for a picture display tube, comprising at least two saddle-shaped deflection coils surrounding the system symmetrically relative to the longitudinal axis and flaring out from the rear to the front, the front end of each coil having a flange-shaped connection portion extending transversely to the tube axis, and between which coils two longitudinal portions extend on either side of a window.
The above-mentioned method is commonly used for winding saddle-shaped coils. In this method the properties of the coil may be influenced by determining the position of the open spaces during the design and by choosing the number of turns per section during winding. In many cases this sprovides the possibility of adapting the distribution of the magnetic flux generated by the coil to the requirements imposed. However, it has been found that this possibility is not adequate in all cases, particularly when more refined corrections are to be performed. Such corrections are necessary, for example, if the east-west raster error is to be reduced in colour display tubes of the in-line type.
Increasingly stringent requirements are imposed on the performance of colour display tubes using electromagnetic deflection units, particularly when they are used in monitors. Stringent requirements are imposed, for example on the shape of the raster.
In conventional TV receivers or in monitors a raster is constituted by causing an electron beam to scan the front plate of the display tube. The (geometrical) raster errors which may occur are north-south raster errors (errors on the upper and lower side of the raster) and east-west raster errors (errors on the left and right-hand side of the raster). In colour display tubes having an in-line arrangement of the electron guns the east-west raster error becomes manifest as a pincushion or barrel-shaped distortion of the left and right-hand boundary of the raster scanned on the display screen.